Understanding Insulin: The Hormone That’s Not Your Enemy

If you’ve spent any time in the fitness or nutrition world, you’ve probably heard insulin framed as the villain—something to “control,” “minimize,” or avoid spiking at all costs. In a recent email Marcus Filly of Functional Bodybuilding pushed back on this narrative, highlighting a common misconception: insulin isn’t the problem—misunderstanding it is.

Let’s break it down in a way that actually helps you make better decisions with your nutrition and training.

What Is Insulin, Really?

Insulin is a hormone produced by the pancreas. Its main job is simple but essential: it helps move nutrients—especially glucose (sugar from carbohydrates)—from your bloodstream into your cells, where it is used for energy or stored for later. Think of insulin as a key. When you eat carbohydrates, your blood sugar rises. Insulin is released to “unlock” your cells so glucose can enter. Without it, that glucose would just float around in your bloodstream, which is exactly what happens in conditions like Type 2 Diabetes. So right away, we can see: insulin isn’t optional—it’s vital.

The Myth of the “Insulin Spike”

In fitness culture, “insulin spikes” are treated like something dangerous. But this is where context matters. Yes, insulin rises after eating—especially after consuming carbohydrates. That’s not a flaw in your body; it’s a feature. It’s how your body manages energy. In fact, insulin also plays a role in: 

• Muscle repair and growth
• Glycogen replenishment (restoring energy in muscles)
• Preventing muscle breakdown

From a performance standpoint, insulin is actually helpful. After a workout, your body is primed to absorb nutrients. A rise in insulin helps shuttle glucose and amino acids into muscle cells, supporting recovery. Avoiding insulin spikes entirely would be like trying to drive a car without ever pressing the gas pedal.

The “Low-Carb Trap”

Filly’s email also touched on what he calls the “low-carb trap”—the idea that drastically cutting carbs is the best way to control insulin and improve health. Here’s the nuance: reducing highly processed carbohydrates (like sugary drinks and refined snacks) can absolutely improve health markers. But eliminating or severely restricting all carbohydrates can backfire, especially for active individuals. Why? Because carbohydrates are your body’s preferred energy source during moderate to high-intensity exercise. Without enough carbs:

• Performance drops
• Recovery slows
• Training intensity suffers
• Hormonal balance can be disrupted

Ironically, going too low-carb can make your body less efficient at handling glucose over time. This is sometimes referred to as “physiological insulin resistance”—a temporary adaptation where your body becomes less responsive to carbs because it rarely sees them. That’s not metabolic damage—it’s just your body adapting to your diet.

Long term, the real costs of a low-carb diet show up the following ways:

• Your body starts to break down muscle tissue to use as fuel
• Cortisol levels rise and stay elevated
• Your metabolism slows as your thyroid down-regulates
• Training quality tanks, which means less progress
• Cravings spike and adherence becomes a daily battle

Insulin Sensitivity: The Real Goal

Instead of fearing insulin, a better focus is improving insulin sensitivity—how effectively your body responds to insulin. When you’re insulin sensitive: 

• Your body needs less insulin to manage blood sugar
• Nutrients are delivered efficiently to muscles
• Energy levels are more stable

When insulin sensitivity is low (often due to inactivity, excess body fat, or poor diet), the body has to produce more insulin to do the same job. Over time, this can contribute to metabolic conditions.

According to Diabetes Canada, lifestyle factors like regular physical activity, balanced nutrition, and maintaining a healthy body weight are key to improving insulin sensitivity and reducing the risk of type 2 diabetes.

What This Means for Your Nutrition

Rather than avoiding insulin spikes altogether, aim for a balanced approach:

1. Choose quality carbohydrates. Focus on whole, minimally processed sources like vegetables, fruits, whole grains, and legumes. Think about carbs this way:
   1. Foundation carbs: sweet potatoes, oats, beans, lentils, whole potatoes. These are high in fibre, provide a high level of satiety, and are rich in micronutrients.
   2. Whole Fruits: Great around training. Fast-digesting, fibre-rich, high in micronutrients.
   3. Minimally processed grains: rice, sourdough, corn tortillas. Fine in your diet, especially at maintenance or if you’re trying to gain weight. Eat less of these if you are trying to lose weight.
   4. Refined and processed: crackers, cereal, candy. Not banned, but low on fibre, volume and easy to over-consume, especially if you’re in a deficit.

2. Pair macronutrients. Combining carbs with protein and healthy fats helps moderate blood sugar and keeps you fuller longer.

3. Time carbs around activity. Eating carbohydrates before or after workouts can support performance and recovery when your body is most ready to use them.

4. Stay active. Exercise—especially resistance training—improves insulin sensitivity.

The Bottom Line

Insulin isn’t the enemy—it’s a critical player in your health, performance, and recovery.

The real issue isn’t insulin spikes from a balanced meal. It’s chronic overconsumption of

ultra-processed foods, combined with low activity levels, that can lead to poor insulin sensitivity over time. So instead of fearing carbs or chasing flat blood sugar at all costs, focus on eating whole foods, training consistently, and supporting your body’s natural systems.

References:

Diabetes Canada (2023), Health Canada (2022), Canadian Society for Exercise Physiology (2021), Filly, M. (2026)